Radiation choke



United States Patent O we g RADIATION CHOKE Marvel W. Scheldorf, Palos Heights, 11]., assignor to Andrew Corporation, a corporation of Illinois Application October 13, 1955, Serial No. 540,239

6 Claims. (Cl. 333-12) The present invention relates to a radiation choke, and more particularly to such choke which is to be applied to a radiating conductor.

In my copending application, Serial No. 527,842, filed August 11, 1955, now U.S. Patent 2,852,774, for a Suppressor-Type Antenna, there was shown an application of a radiation choke to an antenna to isolate one portion of the antenna structure from that portion which was supposed to be the effective radiator. The present invention is directed to the detailed principles of construction of such a radiation choke.

It is therefor an object of the present invention to provide a radiation choke which may be employed to isolate radiation along a conductor or to isolate a portion of a conductor so that its effect on adjacent elements is eliminated.

It is an object of the present invention to provide a new and improved radiation choke.

Other and further objects of the present invention subsequently will become apparent by reference to the following description taken in conjunction with the accompanying drawing, wherein:

Figure 1 is a view partially in cross-section showing the constructional details of the choke comprising the present invention;

Figure 2 is a graph showing several curves illustrating the operation of the invention; and

Figure 3 is a diagrammatic representation of an antenna structure, to which the chokes have been applied to illustrate their effectiveness.

Referring to Figure 1, there has been shown an antenna conductor 11 about which there is located a coaxial conductor or cylinder 12 supported at each end by insulator rings 13. These rings are suitably retained in position by retaining rings 14 and 15 mounted on the coaxial conductor 11 and other retaining rings 16 and 17 mounted on the inside of the cylinder 12. At the center of the cylinder 12 there is located a conductive ring 18, which may be welded or soldered to the central conductor 11. The outer cylinder 12 is likewise suitably connected to the ring 18, which might be by soldering or by means of a fastening device such as a set screw 19. The physical length of the cylinder 12 is one-half wavelength of the radiant energy along the conductor 11. At each end of the cylinder 12 are conductive rings 21 which are suitably soldered or welded to the exterior of the cylinder 12. Mounted on the exterior of the rings 21 are cylindrical members 22 suitably secured to the ring 21 by welding, soldering, or by means of a set screw 23. The cylinders 22 have a physical length of slightly less than one-quarter wavelength, but with the cylinder 12 "have an effective electrical wavelength of one-quarter wavelength. Since the entire unit is grounded at the midpoint of its length, two high impedance points at the ends of the main cylinder 12 are obtained. In other words, the central conductor 11 is connected to the inner cylinder 12 at its center so as to produce two coaxial paths each one-quarter wavelength long, resulting in high impedances at the open ends of these coaxial paths which occur at the extreme ends of the device. Not only is current blocked at the coaxial path, but a high impedance is produced at the terminals equivalent to having an open ended conductor at each end.

In order to illustrate the effectiveness of the device shown in Figure 1, the curve A of Figure 2 shows the E plane radiation pattern obtained by an antenna of the type shown in Figure 3 not having the chokemembers shown in that figure. The antenna, therefore, consisted of a folded half wave dipole antenna 31, having two extension members 32 and 33. This antenna was deliberately designed so as to show the detrimental effects of a rather poor antenna arrangement. While such device would not 'be used by anyone skilled in the art, nevertheless it frequently happens that it is desired to position a half wave dipole antenna on some structure which might have practically the same effect on the half wave antenna as the extension members 32 and 33. The overall physical length of the extension members 32 and 33 was three wavelengths.

When two radiation chokes 10 were applied closely adjacent to the effective ends of the half wave folded antenna, the detrimental effects of the extension portions 32 and 33 were nullified as is apparent from the radiation curve B obtained from measurements under these conditions. Thus, these tests definitely indicate that not only may the radiation choke be used to isolate a portion of a radiating structure, as was done in the copending application above referred to, but is also efiective in maintaining radiation in a particular antenna as illustrated by the diagrammatic arrangement of Figure 3. Thus, it is possible to maintain the radiation from the antenna proper in a direction normal to its axis, irrespective of adjacent supporting structures. The choke is also effective in suppressing higher order pattern variations.

While for the purpose of illustrating and describing the invention a specific embodiment has been shown in the drawing, it is to be understood that such variations are contemplated as may be commensurate with the spirit and scope of the appended claims.

I claim as my invention:

1. A radiation choke comprising a cylinder surrounding an antenna conductor, said cylinder at each end being connected to two larger cylinders extending axially over a substantial portion of said first cylinder toward the center of said first cylinder, said latter cylinders and end connections having an electrical length of one-quarter wavelength, said first cylinder having an electrical length of one-half wavelength of the frequency to be choked on said conductor, and a conductive connection between the center of the first cylinder and said conductor.

2. A radiation choke comprising a cylinder spaced from and coaxially arranged relative to an antenna conductor, said cylinder at each end being connected to two larger shorter cylinders extending axially over a substantial portion of said first cylinder toward the center of said first cylinder, annular end connecting members extending between said larger cylinders and the ends of said first cylinder, said latter cylinders and end connecting members each having an electrical length of one-quarter wavelength, said first cylinder having an electrical length of one-half wavelength of the frequency to be choked on said conductor, and a conductive connection between the center of the first cylinder and said conductor comprising an annular member extending between said conductor and the inside of said first cylinder.

3. A choke for an antenna conductor comprising a cylinder one-half wavelength long, a pair of shorter cylinders arranged concentrically to said first cylinder and extending axially over a substantial portion of said first cylinder from the ends thereof toward its center, a plurality of annular conductive members extending between the ends of said first cylinder and one end of each of said second cylinders, said shorter cylinder and its annular conductive member being substantially one-quarter wavelength long, and an annular conductive member extending from the inner center of said first cylinder to said conductor.

4. A choke for an antenna conductor comprising a cylinder one-half wavelength long, a pair of shorter cylinders arranged concentrically to said first cylinder and extending axially over a substantial portion of said first cylinder from the ends thereof toward its center, a plurality of conductive members extending between the ends of said first cylinder and one end of each of said second cylinders, said shorter cylinder and its conductive member being substantially one-quarter wavelength tong, and a conductive member extending from the inner center of said first cylinder to said conductor, said first cylinder being arranged concentric to said conductor.

5. An antenna conductor assembly comprising an elongated radiating element of greater than one-half wavelength having a halfiwavelength longitudinal portion thereof effectively surrounded by a choke, the choke comprising inner and outer conductors substantially surrounding the radiating element, the inner being one-half wavelength long and the outer comprising aligned spaced segments each approximately one-quarter wavelength long extending axially over a substantial portion of the inner and having the ends of the outer conductively connected to the ends of the inner, the central longitudinal region of the inner being conductively connected to the radiating element.

6. An antenna comprising an elongated radiating element of greater than one-half wavelength having a halfwavelength longitudinal portion thereof effectively surrounded by a choke, the choke comprising inner and outer conductors substantially surrounding the radiating element, the inner being one-half wavelength long and the outer comprising aligned spaced segments each approximately one-quarter wavelength long extending axially over a substantial portion of the inner and having the ends of the outer conductively connected to the ends of the inner, the central longitudinal region of the inner being conductively connected to the radiating element, and means for feeding a signal to be radiated to one of the longitudinal portions of the radiating element extending from the choke, said portion being resonant at the signal frequency, whereby the longitudinal portion so fed is effectively isolated from the other longitudinal portion.

References Cited in the file of this patent UNITED STATES PATENTS 

